The subject matter disclosed herein generally relates to ram air turbine (RAT) actuators, and more specifically a latch mechanism for use in a RAT actuator.
RATs are commonly used on modern aircraft to provide a secondary and/or emergency power source in the event the primary power source is insufficient or fails. A typical RAT remains internal to the aircraft until needed. When additional power is required, a door in the aircraft's fuselage will open and the actuator will deploy the RAT into the freestream air. The turbine is rotated by the freestream air and the rotational power from the turbine is transferred through a drivetrain to be converted into electrical power by a generator or hydraulic power by a pump, or both.
Solenoids are conventionally used to initiate the actuation of a RAT actuator in order to deploy the RAT into the freestream air. Deployment of the RAT requires tripping a release mechanism, known as a latch mechanism. The solenoids trip the latch mechanism, which allows a lockbolt to axially translate and trigger a series of events causing the actuator to extend deploying the RAT. Hydraulic pressure is required to retract the extended actuator and then a biasing mechanism is used to reset the latch mechanism.
The solenoid deployment force must overcome a variety of forces to deploy the RAT. These force may include friction in the latch mechanism, the force necessary to impart slight axial movement of the lockbolt, and the force excreted by the reset plunger. The solenoid deployment forces are typically limited by weight and aircraft power consumption constraints. This limits the permissible opposing force that is exerted by the biasing mechanism. A low force biasing mechanism is commonly used, so as not to require extensive solenoid deployment forces in order to overcome the opposing biasing mechanism. A low force biasing mechanism has minimal force margin which may prove insufficient to overcome various release mechanism forces that can increase as the actuator ages. The inability to overcome these forces may results in higher occurrences of the biasing mechanism failing to reset the latch mechanism and a more robust solution is desired.